The ministry said Monday that about 500 million pounds will be spent to update the Rolls-Royce reactor core manufacturing plant in Derby in central England.

The remainder of the contract is for two reactor cores. One will be for the seventh and last of the Astute class submarines, which do not carry nuclear arms. The other will be for the so-called Successor class, intended to replace Britain's Vanguard submarines which carry nuclear-armed Trident missiles.